The present invention relates to a nut and washer connected as a single assembly with the nut being free spinning relative to the washer.
In fastening workpieces together with threaded fasteners including a nut and a bolt it is frequently desirable to provide a washer between the nut and one of the workpieces. The washer is provided for a variety of purposes including increased load distribution, reduction or control of friction between the nut and engaged workpiece, etc. In many cases it would be advantageous if the nut and washer were provided in an integrated form or as a single assembly of separate components.
It is desirable, however, for certain fastener applications with such a nut and washer combination that the nut and washer turn freely relative to each other during rundown and tightening onto the associated bolt. The free spinning characteristic can be advantageous in reducing and/or controlling the frictional surface forces and thus controlling the relative torque and tension relationship of the fastener to achieve a desired clamp up of workpieces being secured together.
Such nut and washer combinations, i.e. single assembly with a free spinning nut and washer, have been used in industry to reduce the number of separate, single piece items handled by assembly operators and to reduce the number of different parts and part numbers carried for inventory. In the latter assemblies the nut has been of a one piece, generally conventional construction, and different methods have been used to connect the nut with the washer. In one form, the nut and washer are connected by the displacement of metal from either the washer or the nut into a groove or cavity of the other; similarly the connection can be made by forming over an edge or projection of one relative to the other. The different methods allow for the groove, cavity or edge to be either in the bottom of the nut or on the internal diameter of the washer.
Because the latter methods of attachment require permanent metal deformation by forming or displacement, it is usually accomplished prior to heat-treatment and prior to the application of final finishing, such as coating, plating, etc. But such prior attachment of the washer by forming, etc. can result in difficulties because of the additional processing steps necessary after such forming, etc.
For example, the heat-treatment of large nut and washer assemblies can be complicated because of the difference in mass of the parts, i.e. the significantly greater mass of a large nut compared to the relatively smaller mass of the mating washer. During the heat-treatment process the difference in mass between the nut and washer can cause hardness discrepancies from the heating cycle and/or the quench or cooling cycle. It may also be advantageous to have the nut and washer constructed of different materials; but this combination could cause still additional problems where the different materials require a different heat-treat process. In addition, damage to the nut and washer assemblies could occur during subsequent processing and handling resulting in dislodgement or separation of the nut and washer; this could occur, for example, as the assembled parts are batch transported through the different phases of heat-treat cycles, etc.
The forming, etc. process, requiring permanent deformation, to connect the nut and washer may also result in irregularities that cause interference and inhibit the free spinning characteristics of the nut and washer assembly. Thus functional difficulties of the assembly may result from the loss of concentricity between the nut and washer mating surfaces, from variations in metal thickness of the washer material, from variations in relative ductility of the materials and from variations in pressure of the tooling used for forming, etc. in assembly.
It would be desirable to connect the nut and washer into a single assembly after separate heat treatment or after all processing other than assembly is completed and without the requirement for metal forming, etc. by permanent deformation. In the present invention a structure is provided which permits the connection of a nut and washer in a single assembly after all such processing while at the same time eliminating the necessity to connect the nut and washer into a single assembly by permanent deformation through forming, etc.
Thus in the present invention the nut is enveloped or contained in a stamped sheet metal outer cage. The cage is provided with an opening in the bottom or underside larger than the nut thread diameter and has resilient tabs extending in the direction of the nut axis with protrusions extending radially outwardly from the tabs.
The protrusions are constructed to be captured by a shelf or ledge type structure on the internal diameter of the washer and to thereby retain the nut and washer together in a single assembly while permitting free spinning relative to each other.
The method of final assembly, after substantially all processing is separately completed on the nut with its cage and washer, is to push on the top surface of the nut with the tabs of the nut cage centered or concentric with the washer internal diameter. The tabs due to their resilient, springlike characteristics will temporarily deflect radially inwardly permitting the protrusions to be moved or indexed in line with the shelf or ledge on the washer and to be caught thereby when the tabs spring back toward their original positions. Now the washer will be connected to the nut with the connection allowing for free rotation of the nut on the washer during installation of the nut and washer to a stud or bolt and subsequent run-down and tightening. At the same time, the nut with its cage can be disassembled from the washer if desired.
Preferably the nut can be of a laminated structure. In this regard such laminated nuts utilize laminations of hex shaped, hardened coned-disc springs, having a central opening tapped to match threads on an associated bolt. Such nuts have stacked aligned multiple discs retained by a steel outer cage having a hex shape mating with that of the nut. Examples of such laminated nut structures are shown and discussed in U.S. Pat. No. 4,383,787, issued to Reynolds on May 17, 1983. Thus with that type of fastener the retaining cage can be readily formed with the tabs and protrusions noted to facilitate the construction of the assembly with a separate washer as discussed above.
The laminated nut construction has a desired load retention characteristic. In this regard, the laminated nut is free running on the bolt until seated. After initial clamping of the workpieces, a locking force between the nut and bolt results from the application of additional torque and rotation. The additional torque compresses and partially flattens the conical spring discs whereby a mechanical interference occurs between the thread flanks of the nut and bolt. The resultant thread interference and retained spring load between thread flanks resists unloading that might otherwise occur as a result of tensile or vibrational loads. Thus, in a preferred form of the present invention, the laminated nut and attached washer assembly has the advantages of a laminated nut while providing the advantages of ease of operator installation and reduction in parts inventory of the prior nut-washer combinations; at the same time the nut with its cage and washer combination permits separate heat-treatment, finish, etc. of the nut with its cage and washer prior to assembly.
Therefore it is an object of the present invention to provide a new and unique nut and washer combination in which the nut and washer are connected together as a single assembly and are free spinning relative to each other and with the combination including an external cage on the nut operative to secure the nut and washer together.
It is another object of the present invention to provide such a nut and washer assembly in which the nut is a laminated nut structure including a nut member defined by a plurality of laminations and an external cage for holding the laminations together with the cage having resilient connecting means securing the nut and washer as a single assembly while permitting free spinning relative to each other.
It is another object of the present invention to provide a new and unique nut and washer assembly with the nut and washer being connected for free spinning relative to each other.